The overall goal of this program is to develop a new generation of high yield PET radioisotope targets for use with the low energy Tandem Cascade Accelerator (TCA) and with medium energy cyclotrons. Our approach to target design for low energy bombardment has been to develop single foil, conduction cooled window geometries capable of withstanding high thermal and mechanical stresses and to develop solid phase targets which can be bombarded in vacuo without a target window. In all cases, the chemical form of the activity extracted from the target is the same as that produced in existing cyclotron targets. This approach insures that the new targets can be easily interfaced to existing cyclotron targets. This approach insures that the new targets can be easily interfaced to existing radiochemical synthesis systems. In Phase I, a novel conduction cooled foil window design which minimizes mechanical stress on the foil was developed and tested on an N2 gas target for 15O production, a novel cryogenic H218O-ice target for the production of 18F-fluoride was designed and tested, a new technique for efficient extraction of 13N activity from a graphite target was developed, and the design of a windowless solid B203 target for the production of 11C was investigated. In Phase II, the production of clinically significant yields of 15O, 18F, 13N and 11C in these targets will be demonstrated. All target engineering and testing will be performed at SRL using a TCA operating in our laboratory. In a parallel effort, we will investigate the chemical form of activity from the same target materials irradiated with a cyclotron beam at Washington University. The performance of these targets with a medium energy PET cyclotron will also be evaluated.